CD8 T Cell Replicative Senescence: Impact on Aged Humans

描述（由申请人提供）：拟议的研究解决了一系列问题，这些问题来自老年人在其一生中暴露于无数病原体的事实。在某些情况下，这种免疫史导致记忆性CD8 T细胞的扩增，这些细胞已经达到了复制性衰老的阶段。在细胞培养中，与CD28+祖细胞相比，经过多轮抗原驱动增殖达到这种状态的CD8 T细胞表现出不可逆的细胞周期阻滞、CD28基因表达的永久性丧失、细胞凋亡抵抗、应激反应差、细胞因子谱改变和端粒缩短。临床研究已经确定了CD8 T细胞表现出复制性衰老特征与多种健康结果（如对流感疫苗的反应性降低和骨质疏松性骨折）之间的相关性。该研究的中心假设是，体内存在的高比例衰老CD8 T细胞在衰老过程中对免疫和非免疫器官系统产生有害影响。为了进一步阐明CD8 T细胞复制性衰老介导多效生理效应的潜在机制，我们将探讨以下具体目标：(1)确定衰老的CD8 T细胞在免疫功能中的作用。直接细胞相互作用和来自衰老培养的无细胞上清液将评估其对CD4 T细胞帮助、CD8效应功能、抗原呈递和抗体产生的影响。(2)评估基因和非基因操作逆转CD8 T细胞复制性衰老的效果。将比较含有CD28或端粒酶的慢病毒载体，降低氧水平和暴露于雌激素（影响与衰老相关的几种基因）对端粒/端粒酶动力学，种群翻倍，CD8 T细胞免疫功能和免疫调节功能的影响。(3)研究衰老的CD8 T细胞在骨质疏松症中的作用，基于慢性免疫激活对骨完整性的影响和骨髓中细胞因子生成T细胞的鉴定。将比较早期传代和衰老的CD8 T细胞对破骨细胞（骨吸收细胞）和成骨细胞（骨形成细胞）的成熟、分化和功能的影响。体外观察将通过小鼠骨质疏松症模型得到证实。总之，拟议的研究将提供一个无与伦比的机会，以实验解剖人类免疫衰老的几个基本方面的遗传和分子基础，这些方面显著影响健康和寿命。

DESCRIPTION (provided by applicant): The proposed research addresses a series of questions that emerge from the fact that elderly persons have been exposed to a myriad of pathogens over their lifespan. This immunological history leads, in some cases, to the generation of expanded populations of memory CD8 T cells that have reached the stage of replicative senescence. In cell culture, CD8 T cells that reach this state after repeated rounds of antigen-driven proliferation show irreversible cell cycle arrest, permanent loss of CD28 gene expression, apoptosis resistance, poor response to stress, altered cytokine profiles, and shortened telomeres compared to their CD28+ progenitors. Clinical studies have identified correlations between CD8 T cells showing characteristics of replicative senescence and such diverse health outcomes as reduced responsiveness to influenza vaccination and osteoporotic fractures. The central hypothesis of the proposed research is that the high proportion of senescent CD8 T cells present in vivo exerts deleterious effects on both immune and non-immune organ systems during aging. To further elucidate the underlying mechanisms by which CD8 T cell replicative senescence may mediate pleiotropic physiological effects, the following specific aims will be addressed: (1) To determine the role of senescent CD8 T cells on immune function. Direct cell interaction and cell-free supernatants from senescent cultures will be evaluated for their impact on CD4 T cell help, CD8 effector functions, antigen-presentation and antibody production. (2) To evaluate genetic and non-genetic manipulations to reverse CD8 T cell replicative senescence. Lentivirus vectors containing CD28 or telomerase, reduced levels of oxygen, and exposure to estrogen (which affects several genes associated with senescence) will be compared for effects on telomere/telomerase dynamics, population doublings, CD8 T cell immune functions, and immune modulatory functions identified in Aim 1. (3) To investigate the role of senescent CD8 T cells in osteoporosis, based on the well-documented effects of chronic immune activation on bone integrity and on the identification of cytokine-producing T cells within the bone marrow. Early passage and senescent CD8 T cells will be compared for effects on the maturation, differentiation, and function of osteoclasts (the bone resorbing cells) and osteoblasts (the bone forming cells). In vitro observations will be confirmed using a murine model of osteoporosis. In sum, the proposed studies will provide an unparalleled opportunity to experimentally dissect the genetic and molecular basis of several fundamental aspects of human immunological aging that significantly impact health and longevity.